The present invention relates to a flow meter for fluids and provided with a measuring chamber, a measuring organ rotatably journalled therein and a counting mechanism connected with the measuring organ by a magnetic coupling comprising two rotary elements rotatable about a common rotational axis, one of which elements is connected to the measuring organ and the other of which is connected with the counting mechanism, which are separated from one another by a non-magnetic wall and each of which are all provided with two permanent magnets, which are arranged symmetrically relatively to one another with respect to the rotational axis and the magnetic axes of which extend parallel to the rotational axis.
In a known flow meter of this kind, the permanent magnets are arranged in such a manner that their ends facing the non-magnetic wall all have the same polarity. The permanent magnets thus repel one another so that the two magnetic pairs, in the rest position, are displaced relative to one another by a quarter circle.
Tests have shown that a magnetic coupling constructed in such a manner operates unreliably when provided with relatively small one-part permanent magnets of either circular or rectangular cross-section. A magnetic coupling constructed in such a manner is particularly unreliable when abrupt changes in rotational speed occur. This acts particularly disadvantageously for the reason that the drive shaft of the counting mechanism, once the intercoupling has been interrupted, is then no longer entrained with the measuring organ.
This disadvantage could be removed by providing each of the rotary elements with relatively large and powerful permanent magnets. This is, however, impracticable because relatively large axial forces arise in these circumstances and cause correspondingly large frictional forces in the bearings and thus reduce the accuracy of the flow meter.